| Summary: | Fuzzy-ball fluid is a two-phase fluid composed of fuzzy-ball and base fluid. It can enhance oil recovery by approximately 30% after water flooding and polymer flooding, which has been demonstrated in laboratory experiments and field applications. However, the EOR mechanism of fuzzy-ball fluid still needs further research. In this study, the microstructure of fuzzy-ball was observed using optical and cryo-scanning electron microscopy. The EOR mechanism of fuzzy-ball fluid was investigated by the microscopic glass etching model experiment and inter-molecular force calculation. EOR contribution ratio of three parts of fuzzy-ball was evaluated by the single core flooding experiment. Results showed that fuzzy-ball was further subdivided into fuzzy-ball structure and floss structure. Correspondingly, the EOR effects of fuzzy-ball fluid were mainly divided into three parts: (a) base fluid. Emulsification was the main way for base fluid to enhance oil recovery; (b) fuzzy-ball structure. According to the distribution characteristics of residual oil, the EOR mechanisms of fuzzy-ball structure were mainly as follows: wedging displacement for membranous oil, squeezing-carrying mechanism for columnar oil, and extruding-squeezing mechanism for blind-end oil; (c) floss structure. Floss structure enhanced oil recovery mainly through entanglement and carrying mechanism. Moreover, the EOR contribution ratio of base fluid, fuzzy-ball structure, and floss structure are 18.35%, 50.94%, and 30.71%, respectively. This study elucidates the EOR mechanism of fuzzy-ball fluid and provides guidance for its subsequent field application and performance improvement.
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